This invention relates to an optical disc playback device such as a CD (Compact Disc) player, a CDV (Compact Disc with Video) player, an LV (Laser Vision Disc) player or a compatible type player capable of playing back two or more of CD, CDV and LV and, more particularly, to an optical disc playback device capable of detecting a state of a disc which is not set in a normal position on a turntable and thereby preventing damage to the device or the disc due to abnormal vibration and also preventing abnormal reproduction of a recorded signal from the disc.
In an optical disc playback device such as a CD player, a CDV player, an LV player or a compatible type player, as shown in FIG. 2, a disc 10 is mounted by inserting a projection 16 of a turntable 14 in a central opening 12 of the disc 10 and clamping the disc 10 by a clamper 18 on the opposite side of the disc 10.
The size of the central opening 12 of a disc is standardized in such a manner that different types of discs have different sizes, e.g., a CD has a diameter of 15 mm and an LV has a diameter of 35 mm. For this reason, in a compatible type player for, for example, a CD (or CDV) and an LV in which these different types of discs are mounted on the same turntable, as shown in FIG. 3, a projection 20 of a large diameter for mounting an LV thereon and a projection 22 of a small diameter for mounting a CD (or CDV) thereon are formed in the central portion of a tuntable 24. In mounting an LV 28 having a central opening 26 of a large diameter on the turntable 24 of such structure, however, there often occurs a case where, as shown in FIG. 3, the LV 28 is mounted on the turntable 24 with the projection 22 of a small diameter erroneously engaging the central opening 26 and being clamped by a clamper 30 in this state. This is particularly the case with an LV of a diameter of 20 cm. Lacking any means for detecting such abnormal state of mounting, the prior art optical disc playback device continues rotation of the turntable with resulting occurence of an abnormal vibration or a damage to the device or the disc.
Likewise in an optical disc playback device other than a compatible type player such as described above, in a case where, as shown in FIG. 4, a central opening 34 of a disc 32 has a larger diameter than a standard diameter due to error in the manufacture, the disc 32 is likely to be mounted on a projection 38 of a turntable 36 in an offset state and clamped by a clamper 40 in this offset state. In this case, tracking servo cannot work properly with resulting occurrence of an abnormal playback.
It is, therefore, an object of the invention to provide an optical disc playback device capable of eliminating the above described drawbacks of the prior art optical disc playback device and by detecting an abnormal state of mounting of a disc on a turntable and thereby preventing damage to the device and disc due to abnormal vibration and also preventing abnormal playback.